1. Field of the Invention
The present invention relates to packet transfer technologies on networks, and more particularly, to a packet transfer method in which a network is divided into a plurality of network areas and routing within an individual network area and between network areas is performed.
2. Description of the Related Art
In recent years, significant increases in the capacity and bandwidth of communication networks typified by the Internet have been made. Thus, the number of communication apparatuses (Network Elements (NEs)) constituting networks and serving as backbones of such communication networks has been increased, and such communication apparatuses have become complicated.
In general, such a communication apparatus (hereinafter, referred to as a “node”), which is connected to a network for transmitting a user traffic, is also connected to a monitoring network which transmits packets for monitoring the communication apparatus (node). In this case, the node is often controlled using an OSI network on which routing processing can be performed in accordance with the ISO9542 and ISO10589 standards (hereinafter, referred to as OSI protocols) defined by International Organization for Standardization (ISO).
The OSI network adopts a method for dividing the entire network (domain) into a plurality of network areas and managing the plurality of network areas. On the OSI network, packet transfer processing, that is, routing within an individual network area and routing between network areas, is performed individually. Routing within an individual network area is called Level 1 (L1) routing, and routing between network areas is called Level 2 (L2) routing.
FIG. 1 shows the concept of a domain and an network area on an OSI network by way of example.
In FIG. 1, nodes represented by “IS1” are packet transfer nodes having an L1-routing function, and nodes represented by “IS1IS2” are packet transfer nodes having both the L1-routing function and L2-routing function. Nodes represented by “ES” are nodes not having a routing function.
In the example shown in FIG. 1, a domain 3 is divided into a network area 1 and a network area 2.
In the network area 1, ES nodes 141 and 142 and an IS1 node 140 communicate with each other on the basis of ES-IS protocol (ISO 9542), IS1 nodes 130 and 140 are L1-connected with each other, and an IS1IS2 node 110 and an IS1 node 120 are L1-connected with each other. An ES node 121 communicate with the IS1 node 120 on the basis of ES-IS protocol (ISO 9542).
In the network area 2, an IS1IS2 node 210, an IS1 node 220, and an IS1IS2 node 230 are L1-connected with each other, and an ES node 221 communicate with the IS1 node 220 on the basis of ES-IS protocol (ISO 9542).
In addition, the IS1IS2 node 110 in the network area 1 and the IS1IS2 nodes 210 and 230 in the network area 2 are L2-connected with each other (that is, a connection line performing L2 routing is formed). That is, the IS1IS2 nodes within the same network area are L1-connected and L-2 connected with each other.
In accordance with the convention of the OSI protocol, a packet transfer node that performs packet transfer within a network area, that is, an IS1 node having an L1-routing function, is required to hold routing information of all the nodes existing within the network area to which the packet transfer node belongs as the routing information table in a memory of the packet transfer node. Thus, when a node is added to a network area, the addition of the node affects the system resources, such as memory resource, address resources and processing performance resources, of all the packet transfer nodes within the network area. Especially in the case that a node includes both functions of transmitting a user traffic and transmitting a monitoring traffic, for example packets transmitted on the OSI network, the system resources of the node tend to be assigned firstly for the processing of the user traffic and the system resources assigned for the processing of the monitoring traffic are often restricted.
For example, when nodes are added to a network area, the number of nodes to be added is limited to a range not exceeding the number of nodes a packet transfer node having the least memory resource in the network area can handle (for example, the upper limit of the number of nodes on a network can be set to 300). This is because if more nodes than the limited number of nodes are added, the memory resource of the packet transfer node having the least memory resource in the network area becomes insufficient, and the operation of the entire network including the packet transfer node cannot be ensured.
Also, since a node on a network is uniquely identified by a network service access point (NSAP) address and is managed using the NSAP address in accordance with the convention of the OSI protocol, the number of NSAP addresses included within a network area can be limited.
Similarly, since a node performing L2 routing is required to have routing information of all the network nodes that perform L2 routing, the number of nodes (or the number of NSAP addresses) having the L2 protocol can be limited (for example, the upper limit of the number of nodes on a network is set to 250). The IS1IS2 nodes having the L1-routing function and the L2-routing function on the OSI network shown in FIG. 1 are required to hold information on both the L1 routing and L2 routing in the routing information table.
Generally, the number of connected nodes continues to increase in accordance with the continued operation of a network. Thus, as shown by the example of the OSI network, the limit of the number of nodes that can be provided in a network area or a domain is an important issue for network architecture.
As a technology for adding a node onto an OSI network, a technology for adding a node without consuming an NSAP address and for performing routing is disclosed in Japanese Unexamined Patent Application Publication No. 2005-277893.
In known technologies, when a new node is added so as to be adjacent to a network area on a network for which area management is performed, if the network area does not have a memory resource sufficient for adding the node, it is necessary to divide the network area into a plurality of network areas and to cause the new node to be accommodated in one of the divided network areas. Thus, the number of network areas constituting the entire network increases, and managing the entire network becomes complicated.